This invention relates to an actuating mechanism, such as a switch actuating mechanism of the kind comprising a driving member (e.g. a gear member), a driven shaft and a transmission means through which the driven shaft is driven by the driving member through a certain angle of rotation after a predetermined number of revolutions of said driving member, and actuating means carried by said driven shaft and operative at a predetermined angular position of said driven shaft. Such an actuating mechanism is described for example as the counting mechanism in U.S. Pat. No. 4,288,665.
An actuating mechanism of the above kind has application in valve actuators for opening and closing mechanically operated valves. Such valve actuators generally have an output shaft rotatable by an electric motor and drivingly connected to the valve stem. It is conventional to control the energisation of the electric motor at predetermined positions in the travel of the valve in both the opening and closing directions, e.g. at limit positions and predetermined intermediate positions. As actuating mechanism in accordance with the invention can be used to provide such control or to monitor the valve actuator operation in that its driving member can be connected for rotation in a fixed ratio with the valve actuator output shaft and its actuating means arranged to actuate "limit" and/or "intermediate" switches at appropriate points in the travel of the valve stem.
One of the problems with actuating mechanisms of the kind described lies in their adjustment in order to set them up so that their actuating means is operative precisely at a desired point in the travel of the driving member, particularly where the actuating mechanism is used in an environment in which the position of the actuating means cannot be seen as is sometimes the case with valve actuators. The object of the invention is to provide a solution to this problem.
According to the invention, in an actuating mechanism of the kind described an adjustment shaft is provided which can be rotated to rotate the driven shaft through the transmission means, a clutch is connected between the driving member and the transmission means to permit by disengagement of the clutch the adjustment shaft to rotate the driven shaft relatively to the driving member, a radial projection is provided on the driven shaft in a fixed angular relationship to the actuating means thereon, and a removable abutment stop for said radial projection is provided at a predetermined angular position with respect to the axis of the driven shaft to limit the angular displacement of said driven shaft by said adjustment shaft.
Thus with the driving member set at a desired position the adjustment shaft and hence the driven shaft can by virtue of the clutch be rotated relatively to the driving member and such rotation can be continued until the radial projection on the driven shaft comes up against the abutment stop to set the actuating means at a predetermined position for the set position of the driving member. The abutment stop is then removed so that the radial projection and hence the driven shaft can rotate freely.
Conveniently the abutment stop can be provided by a handle fitted to the adjustment shaft for rotating it manually. For example if the handle is in the form of a socket fitting over the end of the adjustment shaft then it can be arranged that the outer surface of the socket is of a sufficiently larger diameter than the outer surface of the adjustment shaft to obstruct the radial projection.
Advantageously the radical projection is in the form of an arm which is spring biased in one direction longitudinally of the driven shaft so that if it is in an angular position to obstruct the fitting of the handle to the adjustment shaft it can be displaced sufficiently to allow fitting and operation of the handle. Thereafter the arm will be rotated from its obstructing position and then be rotated round to its abutting position.
Advantageously the clutch comprises a slipping clutch having a plurality of balls housed in a clutch member on the driven side and spring urged to engage between the teeth of a gear wheel constituting the driving member. For example a plurality of spring urged balls may be provided and which are angularly spaced about the axis of the gear wheel so that one or more but not all of them engage between the teeth of the gear wheel at any one time. Hence the setting of the driven shaft in relation to the driving member, i.e. the gear wheel, is finer than the pitch of the gear wheel teeth.